Many applications today require large amounts of data to be stored and accessed quickly. Magnetic hard disk drives (HDDs) provide dense, non-volatile storage at low cost per bit, but the access times of these devices are intrinsically long, limited by the speed of the moving disk. Other storage components further up the memory hierarchy provide faster access times but at much lower density (e.g., on-chip cache). Aside from solid state memories such as Flash, these alternative technologies require a stable power supply for indefinite storage. And even the non-volatile memories such as flash have limited life cycles.
In the past ten years the search for a fast, non-volatile, dense memory technology has focused a spotlight on a non-volatile random access memory known as the magnetoresistive random access memory (MRAM).
In one approach, an MRAM can be based on a three-terminal memory element that can be switched by a phenomenon known as current-driven domain wall motion [see Fukami, et al., “Low-Current Perpendicular Domain Wall Motion Cell for Scalable High-Speed MRAM, 2009 Symposium on VLSI Technology Digest of Technical Papers, 2009]. This approach includes at least two CMOS access transistors, which can increase bitcell size, and also use non-optimal materials due to shared read- and write-paths.